I'll interject a few points here:

> So my question to the group is why is the metabolic rate the highest at 18C (64.4F)? 

Ummm... it isn't? Where are you getting that from?

> We know that bees need to reach a thorax temperature of 27C (80.6F) to be able to fly and minimum 18C to "pump" flight muscles to actually be able to warm up. 

Again, where are you getting 18C from? Bees are endothermic (using the biology definition: "dependent on or capable of the internal generation of heat") at temperatures far lower than that. 

I think I'm misunderstanding you? This post is confusing. 

In any case, I want to attach the following paper but I don't think it's open access and I checked the regs and because this is an "open group" and not a closed group, I would be breaking the law by sharing it:

Kovac H, Stabentheiner A, Hetz SK, Petz M, Crailsheim K, 2007. Respiration of resting honeybees. J. Insect Physiol. 53, 1250–1261.

In this paper, they measured metabolic rates, as measured by CO2 production, of ectothermic bees. In this case, ectothermic means bees that were at the same temperature as ambient temperature, as opposed to generating heat or endothermic. They found a sigmoidal function that kept increasing until the bee's critical thermal max was reached at around 50C. If nothing else, this paper demonstrates how utterly confusing honey bees are from a metabolic rate perspective. It's in considering this complexity that I hesitate to give "the final say," so to speak, to engineering models that only consider thermodynamics of the cluster and it's enclosure. 

I was using a respirometer to measure metabolic rates of honey bees earlier in the fall and the volume of CO2 released by endothermic bees is huge compared to the volume released when they're ectothermic. Their ability to switch between endothermy and ectothermy and between discontinuous and continuous gas exchange, makes studying honey bee metabolic rates really difficult. It's hard to calibrate such fine machinery to read over such a wide range of values and it's hard/impossible to analyze data that's so variable. That's why this paper looks at respiration in resting, ectothermic bees only. Honey bees are really unique in their ability to so dramatically and quickly alter their metabolic rate. 

Private message me if anyone wants the paper. Apparently I can share it by email to limitless people but I can't share it on the open internet, especially on a site with "evergreen" content. 

Tracey 
Alberta, Canada

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html